Nowadays, more and more electronic devices are adapted to display television programs. This is notably the case of some portable equipment such as personal digital assistants (or PDAs), portable television and laptops. Because of the small size of these items, the size of their TV antennas needs to be reduced as much as possible.
This size reduction becomes an important issue when the frequency of the transmitted TV (RF) signals belongs to the VHF band, which is part of the new off-air standard for TV broadcasting DVB-T. It is noted that the DVB-T standard comprises part of the VHF band (from 170 MHz to 220 MHz), which corresponds to wavelengths approximately equal to 1.5 m, and the entire UHF band (from 470 MHz to 855 MHz), which corresponds to wavelengths between approximately 0.64 m and 0.35 m. If one assumes that the size of the TV antenna must be equal to a quarter wavelength in order to achieve a good TV signal reception, it follows from the above values that the TV antenna size must be of the order of 37 cm if the signal frequency belongs to the VHF band and between 16 cm and 6 cm if the signal frequency belongs to the UHF band. So, if it is possible, although difficult, to design a standard antenna providing an acceptable signal reception over the entire UHF band in a portable device, it is impossible to do so if the antenna also needs to receive TV signals with frequencies belonging to the VHF band, i.e. for frequencies in the UHF and VHF bands.